The invention relates to implantable articles and methods for manufacturing such articles. More particularly the invention relates to a bone prosthesis and a process for manufacturing the same.
There are known to exist many designs for and methods for manufacturing implantable articles, such as bone prostheses. Such bone prostheses include components of artificial joints, such as elbows, hips, knees, and shoulders. An important consideration in the design and manufacture of virtually any implantable bone prosthesis is that the prosthesis has adequate fixation when implanted within the body.
Earlier designs of implantable articles relied upon the use of cements such as polymethylmethacrylate (PMMA) to anchor the implant. The use of such cements can have some advantages, such as providing a fixation that does not develop free play or does not lead to erosion of the joining bone faces postoperatively. However, the current trend is to use the cements to a lesser extent because of their tendency to lose adhesive properties over time and the possibility that the cement contributes to wear debris within a joint.
Recently, implantable bone prostheses have been designed such that they encourage the growth of hard bone tissue around the implant. Such implants are often implanted without cement and the bone grows around surface irregularities for example, porous structures on the implant.
One such implantable prosthesis is a shoulder prosthesis. During the lifetime of a patient, it may be necessary to perform a total shoulder replacement procedure on a patient as a result of, for example disease or trauma, for example, disease from osteoarthritis or rheumatoid arthritis.
In a total shoulder replacement procedure, a humeral component having a head portion is utilized to replace the natural head portion of the arm bone or humerus. The humeral component typically has an elongated intermedullary stem which is utilized to secure the humeral component to the patient's humerus. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is resurfaced or otherwise replaced with a glenoid component that provides a bearing surface for the head portion of the humeral component.
Glenoid components have been designed which include a number of plastic inserts coupled to metal backings. The metal backings are provided to secure the plastic inserts to the glenoid surface of the scapula.
Unfortunately, for a variety of reasons, an implant, for example, a shoulder prosthesis, may occasionally need to be revised or have the old implant surgically removed and a new implant positioned where the prior implant had been removed. Such a procedure is called a revision surgery. In total shoulder arthroplasty, failure of the glenoid component is the primary cause for revision surgery. Primary failure modes are premature wear of the articulating surface and loss of fixation.
When a failed glenoid component is removed, often the subcondylar plate is damaged or missing along with a large defect in the cancellous bone of the glenoid vault of the scapula.
Fixation of a revision glenoid component can be difficult to achieve with a resulting limited bone stock remaining on the glenoid vault of the scapula after the revision surgery has been performed. Often the surgeon has to graft the glenoid defects and convert to a hemi-arthroplasty with a prosthetic humeral head articulating on the remaining natural glenoid articulating surface.
Attempts to provide for an adequate revision glenoid component for revision surgery have met with less than optimal results. For example, current glenoid prosthesis designs include pegged, finned, interference peg and metal back screw type of glenoid prosthesis.
Referring now to FIG. 1, a healthy glenoid fossa 1 which is a portion of the scapula is shown. The healthy glenoid fossa 1 includes a glenoid articulating surface 2 positioned on the subcondylar plate 3. The humeral head (not shown) of a healthy humerus rides against the glenoid articulating surface.
Referring now to FIG. 2, a glenoid 4 is shown with posterior erosion 5 on the glenoid articulating surface 6.
Prior art glenoid components have a generally concave shape with a cylindrical member or peg extending outwardly in a direction opposed to the concave articulating surface. When utilizing a standard glenoid prosthesis to repair a failed glenoid component, the posterior erosion requires that the subcondylar plate be resected or reduced. The subcondylar plate needs to be reamed or resected away to correct the version.
As shown in FIG. 3, the standard glenoid prosthesis 7 rests on only cortical bone 8 along the periphery of the glenoid articulating surface. Not only is the support at the cortical bone areas 8 very limited, the support between the cortical bone maybe full of voids 9 which further reduce the ability of the standard glenoid prosthesis to be properly supported.
Referring now to FIG. 4, a glenoid 10 is shown after removal of a failed glenoid component. The failed glenoid component resulted in a void in the subcondylar plate and the underlying cancellous bone bed.
Referring now to FIG. 5, the failed glenoid of FIG. 4 is shown with a standard glenoid prosthesis 11 positioned over the remaining portions 12 of the subcondylar plate. Again with the configuration of FIG. 5, the standard glenoid prosthesis is only supported at the remaining portions 12 of the subcondylar plate.
Referring now to FIGS. 6, 7, 8, and 9 various prior art attempts at providing a satisfactory glenoid prosthesis are shown.
Referring first to FIGS. 6 and 7, prosthesis 13 and 17 are shown, respectively, for use with PMMA cement.
Referring first to FIG. 6, standard glenoid prosthesis 13 is shown positioned over subcondylar plate 14. A series of pegs 15 are positioned through the subcondylar plate 14 into the cement 16 and cancellous bone bed. As can be seen, the prosthesis 13 requires an intact subcondylar plate 14 to properly support the prosthesis 13.
Referring now to FIGS. 7 and 7A, a finned glenoid prosthesis 17 is shown. The finned prosthesis 17 includes grooves 19 located on fin 18 of the prosthesis 17. The prosthesis 17 is also used with cement 20. As can be seen, the finned prosthesis 17 also requires a subcondylar plate to properly support the prosthesis 17.
Referring now to FIG. 8, an anchor peg prior art glenoid prosthesis 21 is shown. The anchor peg prosthesis 21 includes cement pegs 22 as well as anchor peg 24. The anchor peg 24 may be press fitted for bone ingrowth while the cement pegs 22 are secured to the glenoid articulating surface with cement 23. The anchor peg glenoid 21 also depends on the quality of the subcondylar plate.
Referring now to FIG. 9, yet another prior art glenoid prosthesis is shown as a metal backed glenoid with a screw 25. The glenoid prosthesis 25 includes a metal backing 26 that supports a screw 27 that is fitted into scapula 28. The metal backed with screw glenoid prosthesis 25, as shown in FIG. 9, also requires a well preserved subcondylar plate to properly support the prosthesis 25.
As can be shown in FIGS. 1 through 9, in many cases the subcondylar plate defects and the underlying cancellous bone defects increase the difficulty in achieving appropriate prosthesis fixation and support. A need, therefore, exists for a glenoid prosthesis for use in a patient with a damaged or missing subcondylar plate.